The present invention relates to combustible cartridge case construction, more particularly, it relates to a spring disc securing device for tank ammunition.
Tank ammunition cartridges typically comprise a projectile including an obturator, and a combustible cartridge case assembled to a case base. The inability to chamber 120 mm tank ammunition multiple times without failure has been an ongoing problem for the U.S. Army and for allies who share the 120 mm gun system. One reason tank ammunition cartridges fail is due to the obturator sticking in the gun tube when the cartridge is chambered. Such jamming subsequently may result in destruction of the cartridge when it may be pulled apart upon extraction from the gun tube. Another problem in such cases is that a cartridge failure may also render the tank inoperable. The failure mode is due to flexibility of the case to case base joint that allows the projectile to move farther forward than the gun tube geometry permits. The result of the forward motion is that the obturator sometimes jams within the gun tube.
In the prior art, a spring disc is used to secure the combustible cartridge case to the cartridge base. One such spring disc 10 is shown in FIG. 1. Unfortunately, the prior art design does not offer broad contiguous support of the case nor does it distribute the load evenly, thereby producing an undue amount of localized stress. The prior art spring disc 10 includes a number of separated outer ring leaves 30.
As illustrated in FIG. 2, when installed into a cartridge assembly, a spring disc 10 of the prior art contacts the case only in a limited area 12 around the inner rim 14 of the spring disc, and a portion of the spokes 22. When installed, the outer rim 16 moves away from the cartridge case as indicated by double arrow 21. In the example of a 120 mm cartridge, the outer rim moves above the cartridge surface 20. The result is that loads are concentrated about the inner rim 14, resulting in pinching the case, thereby increasing the likelihood of failure. In a typical cartridge, the localized high stresses are very close to the tensile strength of the cartridge case, thereby increasing the likelihood of failure of the cartridge upon extraction.
In order to improve upon currently available devices, an improved spring disc that uses the same base material and the same plating as the prior art spring disc is needed. Further, since the same or similar gun systems are used throughout the world, it is desirable to minimize the number of new parts.
In an attempt to meet these challenges, a different solution included the use of a glued, snap-in, case-to-case-base joint. The glued snap-in design proved to be unsatisfactory. It provided about three times the tensile load carrying capability of the prior art design, but it was rigid and could not absorb the shock of chambering and extraction, resulting in failure of the case. A variation of the snap-in design used a mechanical interlock for attaching the case to a rubber seal on the case base. It was believed that the rubber seal would provide some degree of shock absorption. It is believed that the mechanical interlock solution is unsatisfactory and is no longer being pursued.
The present invention provides a spring disc for securing a combustible cartridge case to a case base, the spring disc includes a contiguous outer ring including a first plurality of holes and having a contiguous, upwardly curved portion having as outer edge. A contiguous middle ring encompasses a second plurality of holes and a contiguous inner ring, is encompassed by the outer ring and the contiguous middle ring. The inner ring surrounds a central aperture sized to accommodate installation onto a cartridge case member, where the outer ring, inner ring and middle ring operate together so as to support the cartridge case by evenly distributing stresses. A bottom includes the contiguous outer ring, contiguous inner ring and contiguous middle ring. A taper angel xcex8 is built into the bottom and the taper angle xcex8 has a value of at least 1xc2x0 as measured from the bottom extending radially from the center of the contiguous inner ring to the outer edge with reference to a plane parallel to an imaginary plane overlaid on the contiguous outer edge.
In one aspect, the invention provides a spring disc that makes the joint between a cartridge case and case base stiffer to reduce forward travel, yet reduce stresses in the case, without requiring changes to components that are common to 120 mm rounds.
In another aspect of the invention, a spring disc for securing a combustible cartridge case to a case base allows 120 mm cartridges to be chambered and extracted multiple times in a gun tube without separation of the case from the case base.
The spring disc provided by the present invention features a contiguous ring to support a case evenly and reduce localized stresses.
The spring disc provided by the present invention features sufficient stiffness for absorbing chambering shocks, while, at the same time, reducing forward travel of the projectile to prevent the cartridge from jamming in the gun tube.
The spring disc provided by the present invention also features sufficient cutouts and free space under the spring to insure complete burnout of the case so that it is residue free after firing.
The spring disc provided by the present invention features improved stiffness to prevent projectile sticking while providing adequate shock absorption.
The spring disc provided by the present invention also features proven superiority over the prior art design, as shown in testing, by surviving multiple chamber and extract cycles without failure.
Another feature of the invention is that it provides a spring disc that may be used on a variety of tank ammunition cartridges, yet requires no modifications to the prior art case base and seal, combustible cartridge case, or retaining ring.